When starting seeds in the winter to make spring transplants, we count backwards.
The last average annual frost date in zone 7 is April 15th. If I want transplants to put in the ground that weekend I count backwards 6 weeks to the beginning of March to start those seeds.
Not every year is an average year. And, air temperature is not soil temperature.
Consider the fact that tomato and pepper seeds must have bottom heat even if the temperature in your home is 70- degrees F. If the seedling pots are close to an outside window where the temperatures hover around 50 (a compromise between outside temp and inside temps) those seedlings will suffer greatly.
When deciding the plant-out-date for your hard won little plants, check the soil temperature in your area.
For Oklahomans, Mesonet is the go to resource. Here's the Mesonet Soil Temperature link
All states provide this service. Check with your local Extension office to find the resource for your state. It's one more way to ensure plants and gardens that thrive.